There are disk brakes for motorcycles that control a brake disk by gripping the brake disk from both sides using pads.
With reference to Japanese Patent Application No. 3059553,
FIG. 10 is a cross sectional drawing showing a disk brake for a motorcycle.
According to the disk brake 200 for a motorcycle, a caliper body 203 is arranged at an outer periphery 202 of a brake disk 201, an outer pad 206 is arranged between an outer section 204 of this caliper body 203 and the brake disk 201, via an outer back plate 205, and an inner pad 209 is arranged between an inner part 207 of the caliper body 203 and the brake disk 201 via an inner back plate 208.
Together with the outer back plate 205 being pushed out by an outer piston 210, the inner back plate 208 is pushed out by the inner piston 211, and both surfaces of the brake disk 201 are gripped by the outer pad 206 and the inner pad 209.
By causing an upper part 210a of an outer piston 210 and an upper part 211a of an inner piston 211 to project from the outer periphery 202 of the brake disk 201, respective centers of the outer piston 210 and the inner piston 211 are separated from an axle 214 placed towards the outer peripheral edge 155 side of the brake disk 201.
In this way, by separating respective centers of the outer piston 210 and the inner piston 211 from the axle 214 it is possible to increase braking force. Accordingly, it becomes possible to reduce the size of the outer piston 210 and the inner piston 211 while maintaining brake force.
Here, since the upper parts 210a and 211a of the pistons 210 and 211 are caused to project from the outer peripheral edge 155 of the brake disk 201, a bridge section 156 connecting an outer part 204 and an inner part 207 of the caliper body 203 is separated from the outer peripheral edge 155 of the brake disk 201 to the outer side.
Therefore, a distance L from the outer peripheral edge 155 of the brake disk 201 to the inner surface 156a of the bridge section 156 becomes large, and there is a danger that rigidity of the caliper body 203 will be impaired.
In order to preserve rigidity of the caliper body 203, it is necessary to cause the outer surface 156b of the bridge section 156 to project upwardly a lot to make a wall thickness T of the bridge section 156 thick, and this hinders miniaturization of the caliper body 203.
A problem to be solved is therefore to provide a disk brake unit for a motorcycle that maintains brake force as well as enabling miniaturization.